Loud speaker enclosure



Sept. 29, 1964 R, DQNES 3,150,739

LOUD SPEAKER ENCLOSURE Filed Sept. 4, 1962 5 Sheets-Sheet 1 F/GZ k Il

INVENTOR.

@3g-YM 0^/ DOA/ES ATTORNEY United States Patent O LQUD .SPEAKER ENCLSURE RaynionDones, ,S14SheylinDriva El Cerrito, Calif. FiledSeptnt, 1962 Ser. No'. 221,163.

17 Claims; (Cl, 1315-31)T Theapresentfinvention relates to the soundt4 reproduction-art.l More-particularly, this .invention relates to an enclosurefor use inrsound reproduction wherethere is one loudspeaker forlow frequency sounds and one orr It` is` oneobject of this invention to provide means for eticientlymeproducing the low rangeof the. audio spectrum with-.acoustic elements` ofV restricted size.

Itisa-notherobject oftthisrinventionto provide portable cabinets which are readily made from relatively inex-` pensive. components. which may readily be. assembled at.

low cost.

A furtherA objectief; the present invention is to provide` portablesound enclosures which provide ,for high delity reproduction of low frequency i sound.` waves` without; givingan laudible indication ofthe portion ofthe room from which they emanate.

Thgeforegoingnand' other` objectsof my invention Willbe` best; understood by reference to the accompanying drawingsiwhichforma part of-this application Vandwherein like numbers refer-to like structures vand-elements in allof-a saidfdrawings and wherein:

FIGURE 1: isaperspectiveview of an enclosure'made accordingA to .this invention and4 shown partiallydisassembled;v

FIGUREZ issn-enlarged cross-sectional view of zonet 2Al of FIGURE 5;

EIGURE. 3 is` a wiring. diagram showing the electrical relationships of the loud speaker used in the enclosure of;

thisinvention;

FIGURE' 4 is a vertical` cross-sectional view. of the enclosure showndnFlGURE 1. This view is taken alongl thelvertical plane: indicated as 4A-4Bin FIGUREy 5;

FIGURE 5is,a horizontal sectional view takenV along,

theV planeindicated l.aS'SAf-SB `in FIGURE 4;

FIGURE 6 is adiagrammaticillustration of acoustical relation-sy between; components off the enclosureshown in `FIGURES 4j and 5-.

FIGURE: 7 is aperspective viewof another embodi` menti of enclosure according to this invention shown partially disassembled; t

FIG-URE 8mY is a horizontal cross-sectional View of.v the embodiment.. of. FIGURE 7 taken through` a section. as.

SA-SB of FIGURE 4; and

FIGURE 9,is, adiagrarnmatic representation of conditionsmeasured in setting. updimenslons of theienclosures.Y

by av groupof outer chambers as 110A, 10B, 10C and ltiD.`

each formed withI ixedwalls. and a movable rigid wall. A speaker, 1.1 or group ofy speakers is located` within` the. inner ,chamber and ixedly attachedto a fixedA hrm; door member 18 ,of chamber 9 and opens to the air` as. at zone 3,150,739 Patented Sept. 29, lt@

ICC

Z0-exterior to said chamber 9 through an orifice, 89, in said Afloor member.

In the preferred embodiment, below described yin detail,

the interior chamber 9 is formed of four strongly jointed interior partition walls 12, 14, 15 and 16` al1 of the same uniform thickness and flat on their interior and exteriory and firmlyv joined to each other, to a llat oor memberV 18and to a fiat roof-member` 19.

The outer chambers yare formed by rmcorner posts 21, 22; 23, and 24, each post generally square in transverse section and eachvside edge-of each one post straightl andattachedin an air-tight and rigid manner to` the outside of one ofthe-corners formed by the llat partition walls 12, 14, 15 and 16. Each post extendsoutwardly from each partitiony wall corner; each suchpost also is attached firmly and-in air-tightmanner along` tsentire horizontal length .to theadjacent portionolateral extensions 49, 51, 53 and 55 ofimernber` 1S. and149', 51', '53:'V and 55 of member 191which extensionsproject outwardly fromthe outer surface` of walls 15, 12, 14 and. 16 respectively at least to the same extent as. do the posts 21, 22, 23.and 24.

The outer posts and iloor support a group. of llat `lightweight movable piston walls 50., 52., 54, and Se; although.Y

movable with respect thereto, these piston walls aresealed in air-tight manner to the posts, floor and roof neighboring thereto. Each piston walltogether with the neighboring posts, floor member extension. and ceiling member extension and resilient and` exible sealing members attached toeach suchpistonwall, and adjacent partition wall, forms anairftight chamber (except for` the orifice or orifices leading thereinto) as 10A, ltlB, 19C, and 10D, as shown in FIGURES 4 and 5; Each of these` chambers open and Y.communicate only throughl orifices of predeterminedf sizel and position from each of said chambers as 10A, 10B,Y 10C and 10D directly to the inner chamber 9. The diameters of such holes are. at least. 11/2 times the thickness of the walls wherein located.

Accordingv tothis invention the acoustical characteristics ofl the enclosure are chosen as below describedrto be such that the air Within the various chambersof that enclosure and themovable piston walls of such enclosure act` as-a` spring of predetermined inertiav and elasticity to c ausethe movable piston walls as 5t), 52, 54, and 56 tomove outwardandzinwardas a piston as thediaphragm of the` loud-speaker 11` correspondingly moves outwards from andl inwards to chamber 9. Therefore, as provided for-by this enclosureLthe` movement of -these piston walls supplement the airirnoving effectA of the loudspeaker diaphragm and avoids the cancelling effect which otherwise resultsfrom the out-of-phase relationships of the back surface of al speaker cone diaphragm relative to the front surface thereof and the consequentV usual attenuation o f thelow frequency vibrations therefrom.

The orifices in4 each of the partition walls are located so as to. produce in each such wall a geometrical pattern, the center of whichpattern coincides with the center, of gravity of the respective neighboring movable piston walls 50, 52,54, S alonga straight line, asZS and 25? normal to theplane in which such pattern lies. The piston walls member 13 is 32 inches and there is 16 Ainches from the` nearest point of straight edge 2d of post 21 to theY straight edge27 of post 23. There is similarly the same distance of 16 inches from the edge ,28, of post 2,3 to the edge 2? of post 24. A similar distance exists between edge 30 of post 22 and edge 31 of post 24 as well as edge 32 of post 22 and edge 33 of post 21. The partition walls as 12, 14, and 16 in the preferred embodhnent are each made of flat, strong and rigid 1%; inch thick highest grade plywood of uniform thickness. The adjacent partition walls are firmly joined to eachother by jointing and by glue as Well as being similarly firmly secured to the roof member 19 and the floor member 18. In the center of each panel, as 12, eight inches from the top thereof is the center of a 1% inch diameter hole, 35. Eight inches from the bottom of the partition wall 12 is a similar circular hole, 315, which is also 1% inches in diameter and has rounded (1A inch radius on interior, '1/2 inch on exterior) edges. Similar in location and size to the holes 35 and 36 in the partition 12 are holes 37 and 4i) in wall 14 and holes 38 and 41 in wall 15 and holes 39 and 42 in wall 15. FlGURE l shows the enclosure 8 of this invention with the piston wall 56 removed for the purpose of showing the interior structure of chamber lill). Wall 56 is shown in dotted lines in FIGURE 5 to show the position of chamber 10D and slot 48.

In the preferred embodiment each post such as 21 through 24 has straight edges for its full 32 inch length and is 1% inches square in thickness except for the 1A: inch x 1A inch cut-out Where it is glued to the adjacent corner formed by the adjacent partition walls. Each such post is, at each edge thereof neighboring a piston wall, provided with a straight lengthwise slot such as 43 and 44 running the full length of such post for holding a sealing strip element. In the preferred embodiment, wherein the piston walls as 5), 52, 54 and 56 are one inch thick, each said slot has its center 1/2 inch from the outer face, as 45, of the post, as 22. Each slot as 43 is, in such embodiment, A inch thick and 2% inch in depth. The edge of the slot is rounded on the outer portion thereof 46A as well as the inner edge thereof 46B. The other slot, 44, in the same post at its edge 32 has its edges 47A and 47B similarly rounded. All the posts 21 through 24 have similar slots-eg., 43' in post 24-0f the same size in order to hold therein a flexible resilient sealing strip material which is similarly joined to the neighboring mov-A able piston wall at its edge. These slots are all the same size inV order to hold the same size of similarly dimensioned and resilient and flexible sealing strip material with the same degree of resiliency and springiness. These slots extend the full length of each such post and the full Width of members 1S and 19 between such posts. Also, in order to hold the piston walls-through said elastic sealing elements-with such similar degree of elasticity, the tightness of lit as well as the size of the slot is the same for all posts. A slot 48 shown in FIGURES 1 and 5, similar to slot 43, is provided in the lateral extension 55 of the floor member 18 below the piston wall Soifor sealing the oor member 18 to the bottom of each such movable piston wall as well as aiding in the support of each such piston. A similar slot 59 is provided in the lateral extension 49 of floor member 18 below wall 50 for piston wall Stb and a similar slot 60 is Vprovided at extension 53'for the bottom of piston 54. A similar size slot 61 is provided in lateral extension 49' of roof member V19 over Wall member 50 for the top of movable wall Si? and a similar slot 62 is provided at 53' for the topof piston wall 54. Similar slots are provided for the tops and bottoms of each of the acoustical pistons 50, 52, 54 and 56.

The movable piston walls Sil, 52, 54 and 56 are each made of a light weight, air-tight, rigid closed cell plastic polystyrene foam known as Styrofoam 22, a registered trademark of the Dow Chemical Co. 'This foam has a tensile strength (as measured by A.S.T.M. Test D1623fl roY Vspeaker 90 and a tweeter 91.

4 temperature stable, having a heat distortion temperature of 170 F. It has a shear strength (A.S.T.M. Test (3273-53) of about 75 lbs. per square inch. These strength characteristics are chosen to be quite adequate to maintain such rigidity of such walls to permit such walls to act very well as light-weight movable acoustical pistons. In the preferred embodiment each of pistons 50, 52, 54 and 56 is a one inch thick flat board 15% inch wide and 311/2 inches long and weighs a total of 8.5 oz. for a total volume per piston of 233'cubic inches and has a density of only 0.37 gram per cubic centimeter. Re-V silient and flexible sealing strip elements, one end of which is firmly located in slots as 43, 44, 48 and 60-62 with an air-tight seal support the pistons at their sides and bottom and top. This stripping is a flexible, airtight l inch thick, 11/2 inch wide resilient and flexible elastic neoprene closed cell foam. Sealing strip 61 is firmly and air-tightly located in a slot 43A-similar to size and fit and opposite to slot i3-in a vertical edge of piston Sil and extends therefrom to slot 43 in post 22; a similar slot is provided in piston Siliat the other side thereof for sealing strip 62, similar to 61, that provides a similar resilient and flexible yet air-tight seal between Wall 59 and post 24. A similarly located and sealed and dimensioned and resilient and exible vertical sealing strip 64 similarly extends from piston 54 to post 21 while stripping 63 extends from post 23 to piston 54, while similar stripping 65 extends from post 21 to piston 52 and similar stripping 66 extends from piston 52 to post 22. Each piston including S6 has similar slotting and stripping therein at its top, bottom, and sides whereby to provide an air-tight yet flexible seal between each movable piston and its neighboring fixed members atv top and bottom and sides and to provide therewith, an airtight chamber between eachmovable piston and the adjacent partition wall. Stripping is located at the bottom of each piston as stripping 67 for piston 54, stripping 68 forV the piston 54B as well as stripping 69 and 70 at the tops of pistons 54 and Si), respectively. 'In the preferredd embodiment or example herein described the chambers 10A, 10B, 10C and 10D are each inch x 176 inch x 32 inch in size.

The speaker 11 is made up of the standard components used in dynamic loud speakers such as a voice coil 81, a centering spider 83, a flexible annular outer suspension 84, the diaphragm or cone 85, magnet 86 and the basket or frame 87. The frame 87'Vv is secured to the edge 88 of a speaker orifice 89 in the floor member 18 withinV chamber 9. An air-tight connection is made between the outer liexible suspension 84 and the edge 88. Thereby the inner enclosed volume or chamber 9 is closed off from the exterior thereof, e.g.,L at zone 20, by the diaphragm of the speaker 11; thus the enclosed volume formed by the outer chambers 18A, 10B, 10C and 10D fornnwith the interior of chamber 9, exclusive of the volume occupied by the speaker 11, an air-tight enclosure. Y

In .the preferred embodiment the speaker used is a Liensen P-15 LF l5 inch woofer having a 130 square inch cone area and an unbaied resonant frequency of 16 cycles per second, a 40 watt capacity, a 16 ohm irnpedance, and a fiat output characteristicV at frequencies in excess of its resonant frequency.

Power is impressed on the coil of the woofer 11 by pedance of the above described woofer 11 used, the output stage of the Velectrical system represented by Vthe tubes 92 and 93, which are connected to a B+ source 94, provides the input to one phase of the system. In

e orderl 4to provide an attenuation of 12 decibels per octave at a Across-over frequency of Vcycles per second as is used in this preferredembodiment, the inductances With the 16 ohm im-V 95A and 95A each have a value of. 8() millihenries while. thecapacitances of the condenser-96Ais 75 inicrofarads. The circuit illustrated shows the arrangement for stereo, use, withn one channel powered by transformer .97Cjand the ,other channel, powered by transformer 97D'. Where only onechannel is used, the inductance lhas .a value of 40.rnillihenries .(leads 101 `and 102 'lconnectedwhen leads 103 .Y and..104,are ,.disconnected), More simple circuits. may# off course be; used.- with .fewer componentswhere only a 6` decibel per octave attenuation .issatisfactory However,- the particular, electrical .circuitrydat-a is merely exemplary roi the..preferred. embodiment accordingf to this invention. Tables `fon' .Varying .cross-over frequency. are..readily availableto. thosevskilledinfthe art, eg., that puhlishediby. C 8c` M-Coils of 3016 Homes Avenue4 NW., Huntsville, Ala., and inHigh Fidelity Techniques, by-Newithwpublished byR-inehart andk Company, New. York. and. Toronto, 1953,` pages `lilthroixgln..171.

The crosssover. frequency. of g-t-hevabove ,described circuit .shownin FIGURES issuch as fto` provide acrossovenfrom -thewoofer at.100. cycles=per second. This-l avoids, with the, particular aparatus.Sthereinl-disclosed,` any, complication4 due to'V that` the resonant frequency. ofthe speaker in the enclosurefis about 120 cycles per., second:

The acoustical. characteristics of other systemsmay be measured by impressing. various frequencies to the output terminals. 97A andv97B of transformer-.197C and measuring 1j the acoustical output with an. acoustical lWatt-V meterA or` measuring the f impedance.l across the points i. 98A-andtf 98B. The frequency test may` be ativarious `frequencies' between" 16 and 1604 cycles 4persecond with` the outputor impedance-being measured at eachsuch.Y specific;frequency.` There-after, the .inductances,: as 95A. andv 95A- may 'be variedwuntil a-desired acoustical and electrical characteristic is obtained` with.A `variation of 96AY as vneeded.A

In the. particular: example che` twoorilicesas 35. and 36 in wall 12 `and `orifices 37 and 40 in wal-l 14 `and oriiices 38 and 41 in wall 15 are so arranged that astraight line bisecting -t-he` distance] between the center.- ofthose holes -andnormal to -the plane -in `which the centers of.. those tholes lie will .pass througnthe-centerof the .gravityI of the neighboring movable piston wall. It is, of course, Withinzthe :scope `of .thissinvention that, otherr orilice patterns Withs'sirnilar relationships u betweemthe oriiices in the;k partitions-1as` 12,4 14, 15` and 16 Iandfthecenter of gravity-y of. the4 movable` .piston walls; may` alsoabe used. The.arrangenient ofl orifices .of f enclosure. 8 4provides for movement. othe movable pist-on walls..as.5.0,= 52, 54 andif56 a'planey parallelitoathetplane o theneighboring parti-tiomwallcexterior. surface` sont-hatV all parts of eachipiston wall moves.withffhey same amtmntrof.l amplitudes and. `in the same phase. With-each other, especially asV the 'elasticity characteristicsxl ofr all, the sealing. strip ele-ments. are-the` same. and. the dimensions, massl and, thereby,.the-.inertia ofy alllthe` movablepistonwalls are the same.:

According to this inventionnitlhassbeendiscoveredthat an. enclosure'. as.. above described. Will r operate. at .low frequencies according., to the. formula (l) when. certain `specific substitutions. below described be made in.,that formula. Thisipermitshighly eiicientreproduotions of 'low frequency Jsound,equivalent in truenessto ,thatof a horn `bntzrequires vamueh. simpler construction, and. also a .muchsrnallen volume. The. loudspeaker 11. produces excellentresults inutheabotve describedenclosure in the regionfrom 1l to, 100V cyclesper second.

` The. ormula. forY the approximation of the` upper;` limit Y ofY the desiredlminimurn .frequency for the` design of this type `ofenclosure isV as follows.:

wherein;

A is the cross-sectional area yin inchesnofv thetotal of` the `orifices leadingY `from .the inner. chamber 9'Lto the outer chambers 10A, ltifloCandlOD" For ex-` ample, this cross-sectional area wouldbe th'ertotal :of

the. cross-sectional. areas of th'eorices 35,315,137, 38,

The equivalent lengthof. Y the duct L is .the length inf; inches ofl aductr'of `air havingrthe crossr'sectionPfarreiy lthe total. weightA of the*` pistonsSl), 52,;4 54,',56 andfthe; weight ofairfinside` the; cavitiesf1A; 10B; and` 10G;

and'lIiD (f/s x.l6. x `32SJ inthe..-lznrefenr.edfembodiment abovedescri-bedforeach of chambers 10A; 10B; 10C' and. MD) fand. a; pistonend ,'correcticn: The pis'ton i end?correctiony is, for pistonI Walls as. .150; ,52;154; 56;,` the r weight of airainsthe.: hemispheric volume;` onnedfbyfl a., `sphere adiametrahcirclesof whichehas thesarne cross-Y sectionalxarca. as'. the.l totali. crossesectionall: areai (2,000, square inches. in-v the preferred embodiment .i abovedef scribed) measured :parallel to .ltheir.v outer surface; of all the movablepistonsnas 50,152; 54iandf56-t` Theivalueiof; K .isi abovey calculated for dryair. vat 30y Ci Correction'. fory humidity-contenti and temperature: are=well` known,- -to those slcilledsinv the.` art but do Anotzmake, in usualtroorng temperature.- operations, a difference. o'1'3% in.r the value4 of K.

The value f.; isv less'than 16 .cycles/sec. fonthe above described enclosure and. so ris. not` al limiting.` factor. in:` the output. characteristic, of the enclosure.

Thereafter, the holes as 35-42 may.. befenlarged until? the point is reachedwhereat the: frequency. 106tofithe series resonancey hump-.measuredyby impedance:across.y points 98A and 93Br(when switch!1i01;*102fisclosed).` is substantially below the audible limit `(10S-1in FIG?. URE 9). At this pointY the minimum impedance 110V should be at the desired minimum operating. frequency, 16' c.p.s. in the preferredmbodiment, as 8;* Alt -t'hi's-A point the speaker rcsonace in thefenclcsureis aboutV 120- c.p.s. (point`120in FlGUREx); Accordingly,` the\cro'ssover frequency 1112 is chosen: substantially t-herebelow, ie., cps. as abo-ve' described.

Dimensions @prefer-red embodiments as enclosure 8r-y are yso chosen according toformula (l) tobe similarly -suostantiallyL below'the intended lowerlimit` of the in tended operatingrange of frequency of the enclosure,y as 8; soV as tonotfinterfere with the frequencycharacten istics of such enclosurey resul-ting fromA theA elastic charaeteristics-of the sealin-gelementsas 6'11tlzl'r'eughL l0` and` the mass-of the movable piston wallsV associated there.- withv in` the manner hereinv described.-

T-he `-a-bove describedstructure of enclosurev Sie directedf toproduce a resonantl frequency of such structure no greater -thanfl6c;p.s.', the usual -lower limit ofhuman hearing. n rlfhis preferrediembodiment'has a substantiallyv flat output; over the-low'irequency-audio4 range of; 161to`l 100` cycles per second.`r However,- it-is within the sco-pe of this invention that similar structures maybe built* to dimenf sions as expressed-in the above Formula l andprocedure to provide resonant-frequencies lower than l'orA higher, c g., in the'range from 8 to cycles per second .as the lower limit` of operation ofan enclosure as iteinS- above described.' V i The acousticalV output of this enclosure and othen enf closuresmade according tothis system isflat. between itsintended. rangeof operation, c g., 1. 6.to\..100\cyclesaper,v second, in the case` of.` the-enclosureA above described,

j The structure of enclosure 3 also p level of one acoustical watt from 100 c.p.s. down to 16 c.p.s-. when located in a corner.

According to this invention it has been discovered that, as low frequency sound waves bend freely around the orifice corners herein provided, they operate the piston walls of chamber A, 10B, 10C, and 10D of enclosure 8 as though such sound Waves were acting as a perfect fluid. Thus, the compliance of the air in chamber 9 acting through the orifices in the partition walls, with the compliance of the piston wall suspension, acts like a resonator with the mass of the piston walls and the end correction air in contact therewith acting like an extremely elongated duct as 99 of FIGURE 6 in Contact with inner enclosed volume 9. This duct is closed by the pistons 50, 52, 54, 56`represented by 105 in FIGURE 6 and such pistons are resiliently suspended by a mounting system generally shown as 116 in FIGURE 6-comprising the resilient flexible sealing elements as 61-70. The system thus diagrammatically shown as 116 and 105, and 99 in FIGURE 6 has a resonant frequency as shown at 106 in FIGURE 9 and determined as above described. The frequency of the structure mentioned in Formula l above is sufficiently below the frequencies shown as 108 and 106 in FIGURE 9 so as to not limit the desired audio response characteristic of the structure ofrenclosure 8 and similar structures according to this invention.

Accordingly, as the cone diaphragm 85 goes outward and inward relative to chamber 9, the pistons 50, 52, 54, and 56 Will be going outward and inward together in phase with the outward and inward motion of that diaphragm due to the inertia effect of the pistons and cornpliance of the mounting system 116 and the acoustic compressibility of the air within the enclosure volume 9. VThe pistons 50, 52, 54, and 56 each act essentially as an entirely rigid structure with all of the fiexure required for the motion of such pistons occurring at the flexible sealing strips as 61 through 70.

The exterior surfaces of cabinet posts for the top 19 and post and floor edges are finished with conventional finishes or with laminates such as Micarta firmly attached to the fixed enclosure elements, as 21, 22, 23, 24, 18 and 19 to avoid undesired vibrations. The piston walls, as S0, 52, 54, 56 are readily reversed from front to rear sides to vary the designs and colors thereon and in case of damage to the surfaces thereof by the normal physical damage concurrent on the use of any piece of furniture. The slots as 43A in the center of each of the top, bottom and side edges of each of the piston walls and the post slots 43 and 44 and the slots in the lateral extensions as 49 and 49 permit this ready reversibility.

While the above embodiment is shown with four fiat movable piston walls (50, 52, 54, 56) for four secondary chambers (10A, 10B, 10C, 10D) and four partition walis (12, 14, 15, 16) each provided With orifices, it is within the scope of this invention that less than four piston walls and chambers be used With the particular structure above discussed, e.g., with one movable wall. With two movable piston walls as 50 and 54, they are located diametrically opposite from each other, i.e., each movable with its exterior surface located in a plane normal to the same straight line in the same manner as pistons 52 and 56 move inward and outward relative to chamber 9 with their exterior and interior flat surfaces in planes parallel to each other and normal to straight line 25 and pistons 50 and 54 move inward and outward relative to chamber 9 with their interior and exterior fiat surfaces in planes parallel to each other and normal to the same straight line 25.

As shown in FIGURES 7 and 8, enclosure 158, also made according to this invention, has a mid-range speaker as 90 and tweeter as 91 mounted'on a separate rigid wall 115 firmly fixed to member 18' 'and 19'. Partition wall is attachedtair-tight to walls 14 and 16' and members 18 and 19' and has no orifices therethrough providing communication from the exterior of said Wall to the inrovides a sound output terior volume 9. A decorative porous fabric is located on exterior of wall 115. However, the other walls as 12', 14 and 16 and associated cavities 10AA, 10BB, 10C() and associated piston walls and structures are exactly the same as cavities 10A, 10B, 10C of enclosure 8 except for any needed change in value of orifices (as 35-38, 40 and 41) size to provide a satisfactory value of f in Formula 1 as above described; the enclosure 158 is otherwise identical to enclosure 8, and shown in FIG. 7 in the same manner as FIG. l. Y

A tweeter as 91 and mid-range speakers as 90' may also be mounted on top of the fixed roof member 19 as shown in FIGURE 7 in dotted lines within a protectiveand decorative enclosure as 159, also shown in dotted lines, attached to the fixed member of the enclosure, as 19.

Also, a triangular pentagonal or hexagonal cross-sectional shape of chamber 9 and then 3, 5 or 6 walls as( 50, 52, 54, may be used or a circular shape may be used in g lieu of that shown in FIGURE 5 with the movable piston walls of matching shape and performing the same functional relations as above described for the embodiment of enclosure 8. Further, the particular above disclosed size of the inner enclosed volume 9 and secondary enclosed volumes, as 10A, 10B, 10C, 10D and 99, may vary while maintaining the relations between the chambers equivalent to chambers 9vand the sum of chambers such as 10A, 10B, 10C and 10D as above discussed.

Although in accordance with the provision of the patent statutes, a particular preferred embodiment of this invention has been described in detail and the principles of the invention have been described in the best mode in which it is now contemplated applying such principles, it will be understood that the constructions shown and described are merely illustrative and that the invention is not limited thereto and, accordingly, alterations and modifications which readily suggest themselves to persons skilled in the art without departing from the true spirit of the disclosure hereinabove are intended to be included in the scope of the annexed claims.

I claim:

l. A sound reproducing enclosure comprising a first chamber enclosing therein a first enclosed volume and a second chamber enclosing therein a second enclosed volurne,

said first chamber being formed with rigid walls xedly attached to each other, one rigid wall of said first chamber being in contact with an exterior space exterior to said first enclosure and to said second chamber, said one rigid wall of said first chamber having an orifice therein, a loud speaker mounted on said wall and acoustically in contact withand connected to said exterior space through said orifice in said one wall, said loud speaker having a movable diaphragm, said diaphragm having an outer flexible section, said outer fiexible section having an outer edge which outer edge is firmly attached to said one Wall peripheral to the orifice therein, said diaphragm and its edge separating the interior of said first chamber from the said exterior space,

Vsaidsecond chamber comprising rigid walls fixedly attached to each other and adjacent thereto, a rigid I movable wall, iiexible seals between each said movable Wall and said walls fxedly attached to each other, said seals forming an air-tight seal between said adjacent walls and permitting said movable walls to move inward and outward of said second chamber ina direction normal to the outer surface of said movable wall, said first chamber and said second chamber having a common rigid wall fixedly attached Vto neighboring walls Vand said fixed wall havingan orifice therein, and the volume in said first chamber and the'volume in said Vsecond chamber communicating through said orifice, the area of the movable wallbeing several times as great as the area of the movable diaphragm, and the area of the orifice in a the commonrigid wall between the first and second chambers being less than the area of the movable diaphragm.. 4 2'. Apparatus" as in claim" 1 wherein the second enclosed volumej `the yvolume offY 'the first enclosed volume andthe=-area of1 the orificeetherebetween* are related" as expressedlb'y the fllowigifrmulazwhereinn.

fis `substantially below the intendediminimum operating frequencyof lthe enclosure;L

K equals 2,100;

A-is`v` the total Ecross-sectional Sarca-@ini square finches "of the orifice" between fthe? first-*fandf second?y volumes;v

V= isthe ivolume :iinvcubic iricheszbf the enclosure exclusive@l of :the tvolum'e :of: the I. speaker 'c within tithe :first r fenclosed' 3. Apparatus as in claim 2 wherein f=less than 16 and the apparatus has a minimum operating frequency of about 16 cycles per second.

4. Apparatus as in claim 2 wherein the first enclosed volume is a chamber air-tightly sealed from the exterior thereof through a diaphragm of the speaker cone and is provided with no other orifices than those leading to the second enclosed volume.

5. Apparatus as in claim 3 where the second chamber is formed of a plurality of chambers each connected to the first chamber and each of such plurality of chambers is formed with a like rigid-air-tight movable wall each airtightly sealed to air-tight flexible sealing members which are also sealed air-tight to rigid Walls in each of said plurality of chambers, said rigid Walls of each of said plurality of chambers being rigidly connected to a rigid wall of said first chamber, said wall containing an orifice therethrough and wherein A equals the total area of orifices between said first and second chambers.

6. A sound reproducing enclosure comprising a first chamber with rigid walls, a plurality of like second chambers connected to said first chamber, said first chamber having a loud speaker located therein, said loud speaker being fixedly supported within said first chamber and having a movable driven diaphragm operatively open to air, each of said second chambers comprising a movable rigid wall formed with a height and width substantially greater than its thickness and fixed rigid walls, said rigid walls forming with said movable walls air-tight enclosures, means supporting each said movable wall for each of said second chambers and forming an air-tight seal therebetween, the interiors of each of said first chamber and each of said second chambers having a common rigid wall fixedly attached to neighboring walls and each said fixed Wall fixedly attached to neighboring walls and each said fixed wall having an orifice therein, and the volume in said first chamber andthe volume of each said second chamber communicating through each said orifice, the total area of all the movablewalls being several times as great as the area of the movable diaphragm, and the total area of all the orifices in the common rigid walls between the first and second chambers being less than `the area of the movable diaphragm.

7. Apparatus as in claim 6 wherein the orifices leading from said first chamber to each of the second chambers are all of the same size and wherein each of the movable walls have the same dimensions and weight.

10 8. Apparatusas in clairnwherein a plurality of orifices. lead lfrom. said first chamber .into an'adjacent second chamber, said lorifies being p p arranged "in .a ksyrlnmetrical pattern andthe center ofsaidsymmetricalpattern is located, as-measured bya line normal .to 'the plane.` of

whereimfisbelow 16 c.p.s.;

K-equals 2,100;

Alisthe totalcross-sectional area-iti square inches of the orifices between the first and Ysecondchambers;

V is thevolurne, in cubic inches, exclusive of Atliespeakex:

volumewithin the, first chamber;

A of air and havingthe weight of the movable walls and'th'e weightlof "the airv inside the second chamber, andthe weight of.airI in the. hemispheric volume `formed l by a sphere a`- diametral Lcircle of 'which has the same cross-sectional area as said movable walls measured parallel to their outer surface.

10. Apparatus as in claim 8 where f=about 2.2.

ll. A system for high-fidelity sound reproduction comprising a low frequency loud speaker and another loud speaker having a higher frequency range of operation, said first loud speaker and said second loud speaker being connected by an electrical cross-over circuit, and said cross-over circuit is set to attenuate the first speaker input at a frequency below that of the resonant frequency of said enclosure with said loud speaker therein, said first loud speaker being located in a sound reproducing enclosure comprising a first chamber enclosing therein a first enclosed volume and a second chamber enclosing therein a second enclosed volume,

said first chamber being formed with rigid walls fixedly attached to each other, one rigid wall of said first chamber being in contact with an exterior space exterior to said first enclosure and to said second chamber, said one rigid wall of said first chamber having an orifice therein, a loud speaker mounted on said Wall and acoustically in Contact with and connected to said exterior space through said orifice in said one wall, said loud speaker having a movable diaphragm, said diaphragm having an outer flexible section, said outer flexible section having an outer edge which outer edge is firmly attached to said one wall peripheral to the orifice therein, said diaphragm and its edge separating the interior of said first chamber from the said exterior space,

said second chamber comprising rigid walls fixedly attached to each other and adjacent thereto, a rigid movable wall, flexible seals between each said movable wall and said walls fixedly attached to each other, said seals forming an air tight seal between said adjacent walls and permitting said movable walls to move inward and outward of said second chamber in a direction normal to the outer surface of said movable wall, said first chamber and said second chamber having a common rigid wall fixedly attached to neighboring walls and said fixed wall having an orifice therein, and the volume in said first chamber and the volume in said second chamber communieating through said orifice, the area of the movable wall being several times as great as the area of the sions of the enclosure chambers and the orifices are defined by the formula:

A f K rv wherein: f is below 16 c.p.s.; K equals 2,100;

V is the volume, 'm cubic inches, exclusive of the speaker parts volume within the iirst chamber;

A is the total cross-sectional area in square inches of the orifices between the rst and second chambers;

L is the length in inches of a duct of air having the l weight of the movable walls and the weight of the air inside the second enclosed volume and the weight of air in the hemispheric volume formed by a sphere a diametral circle of which has the same cross-sectional area as said movable Walls measured parallel to their outer surface. 13. System as in claim 12wherein the impedance of the speaker in the enclosure changes with frequency and has a minimum impedance at about 16 c.p.s.

16.7Apparatus `as in claim 12 wherein the, speaker has i a resonant frequency in the enclosure and the system has a series resonant hump and said resonant frequency of said speaker in the enclosure istat least 3 oetaves above the frequency of the series resonant hump of said system,

said system has a minimum electrical impedance and said minimum electrical impedance of the system is at a frequency about one octave above said frequency of said series resonant hump of said system.

17. Apparatus as in claim 16 wherein the speaker is supplied electrical energy through a crossover network andthe circuit elements of said crossover network are proportioned so that crossover occurs within an octave of said speaker resonant frequency.

References Cited in the le of this patent UNITED STATES PATENTS 1,988,250 Olson Jan. 15, 1935 2,434,469 Myers Jan. 13, 1948 2,713,396V Tavares July 19, 1955 2,819,772 Bryan Jan. 14, 1958 

1. A SOUND REPRODUCING ENCLOSURE COMPRISING A FIRST CHAMBER ENCLOSING THEREIN A FIRST ENCLOSED VOLUME AN A SECOND CHAMBER ENCLOSING THEREIN A SECOND ENCLOSED VOLUME, SAID FIRST CHAMBER BEING FORMED WITH RIGID WALLS FIXEDLY ATTACHED TO EACH OTHER, ONE RIGID WALL OF SAID FIRST CHAMBER BEING IN CONTACT WITH AN EXTERIOR SPACE EXTERIOR TO SAID FIRST ENCLOSURE AND TO SAID SECOND CHAMBER, SAID ONE RIGID WALL OF SAID FIRST CHAMBER HAVING AN ORIFICE THEREIN, A LOUD SPEAKER MOUNTED ON SAID WALL AND ACOUSTICALLY IN CONTACT WITH AND CONNECTED TO SAID EXTERIOR SPACE THROUGH SAID ORIFICE IN SAID ONE WALL, SAID LOUD SPEAKER HAVING A MOVABLE DIAPHRAGM, SAID DIAPHRAGM HAVING AN OUTER FLEXIBLE SECTION, SAID OUTER FLEXIBLE SECTION HAVING AN OUTER EDGE WHICH OUTER EDGE IS FIRMLY ATTACHED TO SAID ONE WALL PERIPHERAL TO THE ORIFICE THEREIN, SAID DIAPHRAGM AND ITS EDGE SEPARATING THE INTERIOR OF SAID FIRST CHAMBER FROM THE SAID EXTERIOR SPACE, SAID SECOND CHAMBER COMPRISING RIGID WALLS FIXEDLY ATTACHED TO EACH OTHER AND ADJACENT THERETO, A RIGID MOVABLE WALL, FLEXIBLE SEALS BETWEEN EACH SAID MOVABLE WALL AND SAID WALLS FIXEDLY ATTACHED TO EACH OTHER, SAID SEALS FORMING AN AIR-TIGHT SEAL BETWEEN SAID ADJACENT WALLS AND PERMITTING SAID MOVABLE WALLS 